Testes extracts inhibit heart contractions in females of the blood-feeding insect,Rhodnius prolixus

Abstract Myogenic contractions of the heart of the female blood-feeding insect, Rhodnius prolixus (Stål), are inhibited by crude extracts of testes applied directly to isolated dorsal vessels. Dorsal vessels were observed with a stereo microscope and heart beats timed with a stopwatch. In normal Rhodnius saline, hearts contract at 14.8 ± 7.1 beats per minute (n= 45). Crude extracts of the testes and the two male reproductive accessory organs (the opaque and transparent accessory glands) were prepared from previously frozen tissue by homogenizing 5–20 glands in a small glass homogenizer containing Rhodnius saline, centrifuging for 5 min at 2 000 g, and collecting the supernatant. Testes extract as low as 1.0 glands per mL inhibit contractions whereas crude extracts of the opaque or transparent accessory glands have no consistent effect. We refer to this cardiac inhibitor as rhodtestolin (Rhodnius testis inhibitory factor), and discuss its possible effects on the female during copulation.